1. Field of the Invention
The present invention relates generally to a tunable wavelength optical transmission module that is used in the optical network terminal of a wavelength division multiplexing-passive optical network and, more particularly, to a tunable wavelength optical transmission module the wavelength of which can be tuned over a wide wavelength region and which can be implemented at a low price.
2. Description of the Related Art
Recently, with the spread of Digital Groove Service, it is expected that a bandwidth of approximately 100 Mbps per subscriber is required. Accordingly, in place of existing communication methods that cannot provide a bandwidth of 50 Mbps or broader, such as a Digital Subscriber Line (DSL) method and a cable method, Fiber To The Home (FTTH) that can provide a bandwidth of 100 Mbps was proposed. FTTH refers to a subscriber network in which an optical fiber is installed up to the house of each subscriber, and a telephone signal, a facsimile signal, data, a television image, etc. can be transmitted through a single optical fiber. In order to implement such FTTH, an increasing number of subscribers must be accommodated without significantly increasing the scale of installation of the optical fiber and the cost of connecting optical fibers up to the subscribers must be low.
A Wavelength Division Multiplexing-Passive Optical Network (hereinafter referred to as a “WDM-PON”) can be cited as an example of an optical subscriber network that implements FTTH satisfying the conditions. Since the WDM-PON transmits a plurality of multiplexed optical wavelengths over a single strand of optical fiber, subscribers identical in number to the number of optical wavelengths can be accommodated in a single optical line. As a result, the cost of lines and the cost of centralized management at a headend can be reduced. Furthermore, since the subscriber traffic is separated by allocating the optical channels of different wavelengths to the respective subscribers, it is advantageous from the aspects of security and protocol transparency.
The tunable wavelength optical source of an Optical Network Terminal (hereinafter referred to as an “ONT”) that is installed on a subscriber side can be cited as the component of the WDM-PON that most affects the characteristics and cost of the WDM-PON.
An existing tunable wavelength optical source, for example, may be implemented in a single chip by integrating a Semiconductor Optical Amplifier (SOA) and an Electro-Absorption modulator (EA) on an InP substrate. The existing tunable wavelength optical source has a small size because it is formed by integrating devices having different functions on a single substrate. However, the existing tunable wavelength optical source is disadvantageous in that the yield thereof, which determines the price thereof, is very low, and the manufacturing cost thereof is high because an expensive 40-pin butterfly type package must be used due to the necessity for the control of many parts to obtain a desired wavelength.
Another example is a tunable wavelength Laser Diode (LD) that is fabricated by arranging individual elements in an active alignment manner, not by an integration scheme. However, this scheme is problematic in that the price of the package increases due to the active alignment of the individual elements and mechanical and thermal stability is degraded due to the non-integration of the individual elements.
Furthermore, the specifications of the tunable wavelength LD that is required in the operation of a long-distance communication network require an LD that is basically formed by combining the tunable wavelength characteristics of a C-band with the optical/mechanical/thermal characteristics of a DFB-LD device, so that the existing tunable wavelength LD is not suitable for an optical subscriber network that requires a tunable wavelength LD that can be manufactured at low cost through mass production.
As a result, there are demands for an optical transmission module that is suitable for the ONT of an optical subscriber network and can be manufactured at a low price through mass production.